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HID: fix unit exponent parsing 

HID spec details special values for the HID field unit exponent.
Basically, the range [0x8..0xf] correspond to [-8..-1], so this is
a standard two's complement on a half-byte.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Benjamin Tissoires 2012-11-14 16:59:15 +01:00 committed by Jiri Kosina
parent ccdd699411
commit 7746383868
3 changed files with 25 additions and 5 deletions
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16
drivers/hid/hid-core.c
View File

@ -315,6 +315,7 @@ static s32 item_sdata(struct hid_item *item)
static int hid_parser_global(struct hid_parser *parser, struct hid_item *item)
{
__u32 raw_value;
switch (item->tag) {
case HID_GLOBAL_ITEM_TAG_PUSH:
@ -365,7 +366,14 @@ static int hid_parser_global(struct hid_parser *parser, struct hid_item *item)
return 0;
case HID_GLOBAL_ITEM_TAG_UNIT_EXPONENT:
parser->global.unit_exponent = item_sdata(item);
/* Units exponent negative numbers are given through a
* two's complement.
* See "6.2.2.7 Global Items" for more information. */
raw_value = item_udata(item);
if (!(raw_value & 0xfffffff0))
parser->global.unit_exponent = hid_snto32(raw_value, 4);
else
parser->global.unit_exponent = raw_value;
return 0;
case HID_GLOBAL_ITEM_TAG_UNIT:
@ -865,6 +873,12 @@ static s32 snto32(__u32 value, unsigned n)
return value & (1 << (n - 1)) ? value | (-1 << n) : value;
}
s32 hid_snto32(__u32 value, unsigned n)
{
return snto32(value, n);
}
EXPORT_SYMBOL_GPL(hid_snto32);
/*
* Convert a signed 32-bit integer to a signed n-bit integer.
*/

13
drivers/hid/hid-input.c
View File

@ -192,7 +192,6 @@ static int hidinput_setkeycode(struct input_dev *dev,
return -EINVAL;
}
/**
* hidinput_calc_abs_res - calculate an absolute axis resolution
* @field: the HID report field to calculate resolution for
@ -235,17 +234,23 @@ __s32 hidinput_calc_abs_res(const struct hid_field *field, __u16 code)
case ABS_MT_TOOL_Y:
case ABS_MT_TOUCH_MAJOR:
case ABS_MT_TOUCH_MINOR:
if (field->unit == 0x11) { /* If centimeters */
if (field->unit & 0xffffff00) /* Not a length */
return 0;
unit_exponent += hid_snto32(field->unit >> 4, 4) - 1;
switch (field->unit & 0xf) {
case 0x1: /* If centimeters */
/* Convert to millimeters */
unit_exponent += 1;
} else if (field->unit == 0x13) { /* If inches */
break;
case 0x3: /* If inches */
/* Convert to millimeters */
prev = physical_extents;
physical_extents *= 254;
if (physical_extents < prev)
return 0;
unit_exponent -= 1;
} else {
break;
default:
return 0;
}
break;

1
include/linux/hid.h
View File

@ -717,6 +717,7 @@ int hid_connect(struct hid_device *hid, unsigned int connect_mask);
void hid_disconnect(struct hid_device *hid);
const struct hid_device_id *hid_match_id(struct hid_device *hdev,
const struct hid_device_id *id);
s32 hid_snto32(__u32 value, unsigned n);
/**
* hid_map_usage - map usage input bits